This invention relates to emergency evacuation equipment for aircraft, in particular, to inflatable aircraft evacuation slides, life rafts, as well as other inflatable structures.
The requirement for reliably evacuating airline passengers in the event of an emergency is well known. Emergencies at take-off and landing often demand swift removal of the passengers from the aircraft because of the potential for injuries from fire, explosion, or sinking in water. A conventional method of quickly evacuating a large number of passengers from an aircraft is to provide multiple emergency exits, each of which is equipped with an inflatable evacuation slide, which often doubles as a life raft in the event of a water evacuation. These evacuation slides are most commonly constructed of an air-impervious coated fabric material that is formed into a plurality of tubular members. When inflated, these tubular members form a self-supporting structure with a slide surface capable of supporting the passengers being evacuated. In addition to being air-impervious, the fabric material from which the tubular members are constructed must meet FAA specification requirements of TSO-C69c for resistance to radiant heat, flammability, contaminants, fungus and other requirements.
Although evacuation slides permit passengers to quickly and safely descend from the level of the aircraft exit door to the ground, the requirement that each and every aircraft exit door be equipped with an inflatable evacuation slide means that commercial aircraft must devote substantial payload capacity to the carrying of multiple evacuation slides. Accordingly, there has long existed the desire in the industry to make the inflatable evacuation slides as light as possible. A significant portion of the weight of an emergency evacuation slide is the weight of the slide fabric itself. Accordingly, various attempts have been made to reduce the weight of the slide fabric. One accepted method has been to reduce the physical size of the structural members of the slide by increasing the inflation pressure. Increased inflation pressure, however, causes greater stress on the slide fabric and, therefore, the benefit of the reduced physical size is at least partially cancelled out by the need to use a heavier gauge of slide fabric. Current state of the art slide fabric consists of a 72×72 yarns per inch nylon cloth made of ultra-high-tenacity nylon fibers. This 72×72 base cloth has a grab tensile strength of approximately 376 lbs in the warp direction and 326 lbs in the fill direction (as used herein grab tensile strength refers to the strength measured by grabbing a sample of fabric, typically 4 inches wide, between a set of one inch wide jaws and pulling to failure.) The base cloth is covered with multiple layers of an elastomeric polyurethane coating on one side and a radiant-heat resistant aluminum/thermoplastic polyurethane (TPU) layer on the other. This results in a strong, but heavy fabric, having a grab tensile strength of approximately 391 lbs in the warp direction and 389 lbs in the fill direction, but an areal weight of 7.0 oz/yd2 or more. As can be determined from the foregoing, the coatings do not contribute significantly to the strength of the fabric.